Showing papers in "Optics and Laser Technology in 1973"
TL;DR: In this article, a bi-directional laser Doppler velocimeter utilizing optical frequency shifting has been developed for velocity measurements in reversing flows, highly turbulent flows, two-phase flows, and boundary layers.
Abstract: A bi-directional laser Doppler velocimeter utilizing optical frequency shifting has been developed. Optical frequency shifting is achieved by using a rotating radial grating. A high diffraction efficiency permits the system to be used in the fringe mode. The zero velocity frequency shift can be varied from 0.1 to 2.5 MHz with a stability better than 0.2%. Important applications are velocity measurements in reversing flows, highly turbulent flows, two-phase flows, and boundary layers. The system described may also be used for vibration analysis. Experimental results are presented.
34 citations
TL;DR: In this paper, a fluid velocity meter is described, which operates by measuring the time taken for individual dust particles carried in the flow to travel between two points in space, by using a laser to produce two light beams parallel to one another and approximately normal to the flow direction.
Abstract: A fluid velocity meter is described; this operates by measuring the time taken for individual dust particles carried in the flow to travel between two points in space. A laser is used to produce two light beams parallel to one another and approximately normal to the flow direction. These beams are focused to two point or line foci in the region of interest: these foci are separated by a distance of the order of 1 mm in the flow direction. A particle crossing both foci in succession gives two scattered light pulses, and the time interval between these is measured by an oscilloscope or digital chronometer. The particles are natural dust particles occurring in the laboratory air or tap water. As in Doppler and fringe anemometers, the advantage of the laser is its spatial coherence: it enables extreme intensity to be obtained in small, well-defined regions. The instrument might be described as a fringe anemometer in which all the light is concentrated into the two end fringes, the others being eliminated.
27 citations
25 citations
TL;DR: In this paper, a grating is recorded on a photo-resist coated specimen and re-illuminated with the interference pattern used to form it, and live fringes corresponding to displacements can then be observed as the specimen is loaded.
Abstract: A grating is recorded on a photo-resist coated specimen and re-illuminated with the interference pattern used to form it. ‘Live’ fringes corresponding to displacements can then be observed as the specimen is loaded.
25 citations
TL;DR: In this paper, a theoretical method for the calculation of the profiles of holographic diffraction gratings produced in photo-resist is presented, which is shown to give results in agreement with all experimental observations of such profiles.
Abstract: A theoretical method is outlined for the calculation of the profiles of holographic diffraction gratings produced in photo-resist. This method is shown to give results in agreement with all experimental observations of such profiles. Consideration is then given to the flexibility of arrangements for the formation of holographic gratings and an experimental system is discussed which fully utilizes this flexibility. The wide range of profiles which may be generated with such a system is demonstrated. Finally a theoretical programme of investigation is suggested which may well make possible the formation of holographic gratings of greatly improved spectral performance.
18 citations
IBM1
TL;DR: The use of high power laser beams in part identification is particularly applicable where materials are sensitive to mechanical stress, and for parts which require a very durable identification mark to withstand manufacturing processes as discussed by the authors.
Abstract: The use of high power laser beams in part identification is particularly applicable where materials are sensitive to mechanical stress, and for parts which require a very durable identification mark to withstand manufacturing processes. The printing of part numbers with high power lasers has been investigated for two materials: silicon (in a crystalline form) and ferrite. The parameters of the method have been determined, and it has been applied to silicon water and magnetic head identification. A prototype system printing a seven digit part number on silicon wafers is described in detail.
14 citations
TL;DR: In this article, the formation of Moire patterns by doubly exposed photographs of projected interference fringes is analysed in detail, and possible applications of these patterns for the measurement of surface deformation and vibration, phase object visualization and height contouring are examined theoretically and experimentally.
Abstract: The formation of Moire patterns by doubly exposed photographs of projected interference fringes is analysed in detail. The possible applications of these patterns for the measurement of surface deformation and vibration, phase object visualization and height contouring are examined theoretically and experimentally. The described methods are closely related to holographic techniques, but they are usually simpler and applicable in unfavourable environments.
13 citations
11 citations
TL;DR: In this article, a simple holographic recording of a photo-elastic object under stress allows the isochromatics to be observed by double-exposure interferometry: a second traverse of the wavefront through the object after a 90° rotation of its polarization by a Faraday cell eliminates the unwanted isochromeatics.
Abstract: A simple holographic recording of a photo-elastic object under stress allows the isochromatics to be observed. The isopachics are obtained by double-exposure interferometry: a second traverse of the wavefront through the object after a 90° rotation of its polarization by a Faraday cell eliminates the unwanted isochromatics.
10 citations
TL;DR: Synthetic holograms are a successful means of testing optical elements but may be subject to plot distortions which can be determined by plotting linear gratings, so corresponding non-linear co-ordinates are taken as the basis for the computation of the holograms.
Abstract: Synthetic holograms are a successful means of testing optical elements. They may, however, be subject to plot distortions which can be determined by plotting linear gratings. To compensate for these plotting errors the corresponding non-linear co-ordinates are taken as the basis for the computation of the holograms.
8 citations
TL;DR: In this paper, the breakdown region was observed by recording infinite fringe, interferometric, diffuse holograms with a singlemode ruby laser of 100 ns FWHM pulse length.
Abstract: Air breakdown at pressures of 300 and 753 torr was produced by a 28J, 40 ns FWHM neodymium glass laser focused with a 100 mm focal length lens. The breakdown region was observed by recording infinite fringe, interferometric, diffuse holograms with a single-mode ruby laser of 100 ns FWHM pulse length. The two lasers were synchronized to examine the time region from R-t diagram was found to be in excellent agreement with the weak spherical blast wave theory of Sakurai. The radial density profile of the shock wave was determined by an Abel inversion of the fringe pattern. Both the R-t function and the density profile were calculated using a one-dimensional, hydrodynamic model and good agreement was obtained.
TL;DR: The organization of a random access read-write-erase holographic optical memory is described, and estimates are given for the characteristics required of a reversible holographic storage material suitable for this application.
Abstract: The organization of a random access read-write-erase holographic optical memory is described, and estimates are given for the characteristics required of a reversible holographic storage material suitable for this application. The characteristics of photo-chromic, thermo-chromic, and electrically controlled materials are surveyed to indicate how far existing materials satisfy, or could be developed to satisfy, the requirements of fast optical information storage. A figure of merit is defined to indicate the relative value of existing materials for storage applications.
TL;DR: In this paper, a method of evaluating time-average holograms which gives the vibration amplitudes of an object is described, based on the holodiagram, from which a value of sensitivity (k value) is obtained.
Abstract: A method of evaluating time-average holograms which gives the vibration amplitudes of an object is described. The method is based on the holodiagram, from which a value of sensitivity ( k value) is obtained. For sinusoidal vibrations of an object, a k values are calculated from the roots of the zero order Bessel function; these give the values of the vibration amplitude at the dark interface fringes directly by multiplication with the wave-lenght of the laser light and appropriate k value. a k values are tabulated for the first twenty fringes. a He values which incorporate the wavelenght of the commonly used He-Ne laser are also tabulated. The evaluation of a hologram of a metal sheet is described. Finally the difference between the position of fringes obtained from objects with sinusoidal and square-wave amplitudes of vibration is shown.
TL;DR: It is shown that there may be major problems in the use of mtf's in assessing visual systems because of the coherence of coupling between the visual aid and the refraction optics of the eye.
Abstract: It is shown that there may be major problems in the use of mtf's in assessing visual systems because of the coherence of coupling between the visual aid and the refraction optics of the eye. A simple computer program has been set up to help study the errors in predictions of retinal image quality made from mtf measurements. This can be used to produce complex amplitude spread functions cheaply for each element of a system and for cascaded systems. Mtf's derived from multiplying the individual mtf's of a visual aid and of the eye's refraction optics are compared with those derived from complex amplitude wavefront analysis
TL;DR: In addition to the underformed and deformed object, a third hologram was recorded during the deformation process, on the same holographic plate, marking parts of the test object which have not moved.
Abstract: In addition to holograms of the underformed and deformed object, a third hologram is recorded during the deformation process, on the same holographic plate: this marks parts of the test object which have not moved The zero order fringe, which corresponds to zero motion, is reconstructed from the triple-exposure hologram with much greater intensity than the fringes of higher order
TL;DR: In this article, the results of computer calculations concerning the reflectivity in the stopband at normal incidence are given for periodic multilayer systems made out of layers of ZnS and MgF 2 of equal optical thickness.
Abstract: The results of computer calculations concerning the reflectivity in the stop-band at normal incidence are given for periodic multilayer systems made out of layers of ZnS and MgF 2 of equal optical thickness. General formulae are derived to distinguish between the maxima and minima of the reflectivity at the centre of the stop-bands and for the calculation of the width of the stop-band of higher order mirrors as a function of the wavelength. The bandwidth of higher order mirrors and the reflectivity at the centre of the stop-band are presented in a number of graphs for systems with up to 18 layers on substrates with varying refractive index. Quarter-wave layer anti-reflection coatings are treated as special cases. The process of designing laser mirrors can be simplified using the graphs. They may also be useful during the evaporation process when thickness monitoring is done by optical methods. An example of a partially reflecting mirror is given. This uses a flat minimum of reflectivity at the centre of the stop-band to obtain an almost constant reflectivity over the total width of the stop-band.
TL;DR: A multi-level display system is described which permits the recording of non-optical holograms with some control of the spatial frequency response, and a marked improvement in the optically reconstructed image is obtained.
Abstract: A multi-level display system is described which permits the recording of non-optical holograms with some control of the spatial frequency response. A marked improvement in the optically reconstructed image is then obtained.
TL;DR: In this paper, the authors review some of the applications which have been reported so far and also consider future applications and consider the topographies which are generated by the technique and their relevance to device manufacture.
Abstract: It is now apparent that ion beams have a role to play in the machining and polishing of optical components. In this paper we review some of the applications which have been reported so far and also consider future applications. Since ion beam machining is not a passive process we consider the topographies which are generated by the technique and their relevance to device manufacture.
TL;DR: In this article, the application of reference fringes in double exposure holography of transient phase objects is described, including selection of fringe patterns and fringe number densities suitable for the quantitative analysis of the hologram.
Abstract: This paper describes the application of reference fringes in double exposure holography of transient phase objects. This includes selection of fringe patterns and fringe number densities suitable for the quantitative analysis of the hologram. Methods of realizing different reference fringe patterns are presented. As the focus of the interference fringes depends on the optical arrangement, different systems are discussed.
TL;DR: In this paper, the effects of new high power systems on man producing reactions similar to those of severe x-ray burns were investigated. But no experiments have been done to establish this.
Abstract: There is much concern about the effects of new high power systems on man producing reactions similar to those of severe x-ray burns. No experiments, however, have been done to establish this. Piscosecond, neodymium laser impacts with pulse energies varying from 125–500 μJ were done on the skin of a single volunteer and observed over a period of two years. Nonspecific, mild, transient, inflammatory reactions were found.
TL;DR: In this article, a laser Doppler system has been developed at Southampton University that gives an instantaneous velocity record for studying reversing velocities, and the optical principles needed for efficient design of the instrument are described.
Abstract: For studying reversing velocities, a laser Doppler system has been developed at Southampton University that gives an instantaneous velocity record. This article describes the optical principles needed for efficient design of the instrument.
TL;DR: It is shown how the insertion of a suitable spatial filter in the Fourier transform plane can reduce the unwanted cross-cor correlation signal between dissimilar patterns to zero, without removing the desired auto-correlation signal between similar patterns.
Abstract: Conventional holographic pattern recognition systems suffer from the disadvantage that, in dealing with highly ordered patterns such as Arabic numerals or the letters of the Roman alphabet it is sometimes impossible to distinguish between patterns with a high degree of similarity (eg the capital letters ‘E’ and ‘F’ or ‘B’ and ‘P’) The present paper analyzes a simple case and shows how the insertion of a suitable spatial filter in the Fourier transform plane can reduce the unwanted cross-correlation signal between dissimilar patterns to zero, without removing the desired auto-correlation signal between similar patterns Although no attempt is made to generalize the analysis, it seems probable that in cases involving the recognition of a small number of patterns with a strong ‘family resemblance’ a compromise filtering arrangement could be developed which would lead to a substantially improved performance
TL;DR: In this article, the effect of high power CO 2 laser on man's coagulation necrosis was investigated, and it was shown that repeated impacts of 30 mJ pulses with 100 kW caused non-specific superficial coagulations necrosis which healed promptly.
Abstract: The new TEA (transversely excited atmospheric pressure) CO 2 laser can produce ionization of air. No information is as yet available of the effect of this new high-power output laser on man. Repeated impacts of 30 mJ pulses with 100 kW, which produced ionization of air, caused non-specific superficial coagulation necrosis which healed promptly.
TL;DR: In this paper, a report on the laser system used at the Kiev Institute of Oncology for investigating the antitumour action of laser radiation is presented, both experimental work and treatment of patients are described.
Abstract: A report on the laser system used at Kiev Institute of Oncology for investigating the antitumour action of laser radiation. Both experimental work and treatment of patients are described.